Fixed|Savegame Tool: Translation of native ver 13 map URIs

It appears the episode and map numbers in this save format version
are not consistent, e.g., all variants of Doom2 and Hexen are marked
with a non-zero episode number...

In order to translate savegames correctly it is now imperative that
the game identity key is specified, otherwise the format translator
won't know how to transform the episode and map numbers so that they
make sense.